Electrochemical elements such as a lithium ion secondary battery and an electric double layer capacitor have advantageous characteristics that they are small, lightweight, their energy density is high, and they can be repeatedly charged and discharged, and accordingly their demand is expanding rapidly. The lithium ion secondary battery has a relatively large energy density, and it is used in the fields such as cellular phones and notebook personal computers, meanwhile the electric double layer capacitor can be rapidly charged and discharged, and it is used as a memory backup small power source in personal computers and the like. Furthermore, the electric double layer capacitor is expected to be applied as a large sized power source for electric vehicles. Moreover, the redox capacitor using the oxidation-reduction reaction (pseudo electricity double layer capacitance) of the surface of a metal oxide or a conductive polymer also attracts attention because of the size of its capacitance. As for these electrochemical elements, along with the expansion of their applications, further more improvements are required for lower resistance, higher capacitance, more excellent mechanical properties and the like. Under such circumstances, in order to enhance the performances of electrochemical elements, various improvements are also made in the materials which form electrochemical element electrodes.
The electrochemical element electrode is, in general, made by laminating active material layer, which are formed by bonding electrode active materials such as activated carbon and lithium metal oxide and electric conductive materials, on a collector.
Patent Documents 1 and 2 disclose a method of pressing and forming composite particles obtained by bonding particulate electrode active materials and particulate electric conducting auxiliary agents with a binder, and thereby obtaining active material layer. The composite particles used in the Patent Documents 1 and 2 have the structure where particulate electrode active materials and particulate electric conducting auxiliary agents are distributed uniformly in the composite particles.
Further, Patent Documents 3 discloses a method where a slurry mixed material containing electrode active materials, thermosetting resin and solvent is formed, and this mixed material is granulated by the spray-drying method to obtain composite particles, and the composite particles are fixed on a collector by hot pressing, roll pressing, or other means to form active material layer. The particles obtained in the Patent Documents 3 are hollow particles having the husks formed with bonded particulate electrode active materials.
However, in the electrochemical element obtained by use of the electric active layer formed of these particles, the internal resistance becomes high, and accordingly, only electrochemical elements with small capacitance have been obtained.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2005-78943    [Patent Document 2] U.S. Patent Publication No. 2005/0064069    [Patent Document 3] Japanese Unexamined Patent Application Publication No. H09-289142